The present invention relates to a battery management system for a battery module comprising a plurality of cells connected to one another which each have a positive and a negative terminal. The invention is in particular concerned with a battery management system which is used with accumulators especially lithium ion cells for forming a traction battery or a traction battery module for vehicles with an electrical drive drain. Such battery modules can for example be used in electrical vehicles, hybrid vehicles with combustion engines or hybrid vehicles with fuel cells, can however also be used for other purposes, for example for stationary applications or for small traction applications, such as for example in a wheelchair.
The battery management system in accordance with the invention is preferably used with battery modules which are based on lithium ion cells, however, any other available rechargeable battery cell can in principle also be used.
A battery module system, which can for example be built up from a plurality of like battery modules, can for example be designed to cover a power range with an energy content between 1 kWh and 400 kWh or more and can straightforwardly operate in a voltage range between 12 and 800 V. A battery module can for example be designed with twelve individual cells each having a cell voltage of 3.6 V and a capacity of 40 Ah in order to build up a battery module having a total energy content of 1.728 kWh which, depending on the interconnection of the individual cells, has output voltages in the range from 10.8 V to 43.2 V with capacity extraction in the range between 160 Ah and 40 Ah. By way of example with a 3s4p connection, i.e. with four respective cells connected in parallel which are connected three times in series after one another an output voltage of 10.8 V (3×3.6 V) can be generated and a battery module of this kind then enables a capacity extraction of up to 160 Ah. With the configuration of 12s1p, i.e. with twelve cells in series, an output voltage of 43.2 V can be achieved (12×3.6 V) and a current extraction of 40 A for one hour is possible. In general the notation: XsYp has to be understood in such a way that X recites the number of cells in series and Y the number of cells in parallel. Through the circuit variants the possibility also exists of obtaining different module voltages with the same module size and the same basic construction.
In order to achieve higher voltages a corresponding number of battery modules can be connected electrically in series, the connection of the individual battery modules to one another can also take place in accordance with the pattern XsYp.
A reference system for use in electrical battery compact vehicles can for example be orientated on the following key data: total energy content of modules 13.824 kWh (i.e. eight battery modules each having 1.732 kWh), voltage level 400 V and continuous power±20 kW. In this connection it should be noted that for the generation of a voltage level of 400 V it can be necessary to step up the total output voltage of the battery with the aid of an inverter and/or a transformer. For example when using eight battery modules of the above-named kind in a 6s2p configuration with 21.6 V output voltage per battery module, a total output voltage with a series circuit of all eight battery modules of 8×21.6 V=172.38 V is achieved.
Even though a battery module of this kind may be designed for a continuous power of ±20 kW nevertheless peak powers of for example 100 kW can be demanded in short term from the battery for example for acceleration purposes, whereby excellent acceleration values can be achieved. Furthermore, charging can be operated with a charging power of for example 40 kW.
The above quoted values are simply named as an example, but on the other hand represent values which can entirely be achieved with commercially available lithium ion batteries.
Basically the technology of the battery design which appears most suitable in accordance with the criteria of the technical potential can be used at the cell level, such as for example energy and power density, reliability and working life, cost potential and resource availability. At the system level or module level the reliability, the long working life and comfort in operation must also be taken into account. Furthermore, the additional measures which are required to achieve a functioning battery system should involve a minimum of additional cost, weight and volume. Such additional measures relate for example to the electrical management of the battery module, to the thermal management of the battery module, to the integration at the cell level and module level and also to the integration into a vehicle.
In order to guarantee a long working life of the battery cells and in order to ensure that the individual charging and discharging rates of the battery cells do not exceed of fall short of preset values it is known to provide battery management systems for the operation with the battery modules.
In order to carry out a check of the individual battery cells in operation the cell voltages are regularly measured and if necessary investigated for possible faults. Should a fault be detected then a corresponding indication is sent by the battery management system to the user and/or to an evaluation device and in the worst case the battery module is brought into a safe condition.
Since a vehicle is as a rule not permanently in operation, the battery management system is normally placed in a rest state when the vehicle is switched off, and the system is regularly started again briefly after a period of time in order to ensure with long periods of non-use that individual battery cells do not drop below a preset minimum voltage and in order to then place all the cells in the same state of charge.
The invention is based on the object of making available an improved battery management system which is of compact construction, operates very reliably and is relatively simple, and which makes it possible to evaluate the thermal and electrical parameters of the individual battery cells.
In order to satisfy this object a battery management system is provided for a battery module having a plurality of battery cells which each have positive and negative terminals. The battery management system is arranged on a circuit board which has a plurality of electrical contacts which can be brought in direct contact with conductive elements of the battery cells. The conducting elements are formed by the terminals of the battery cells of the battery module and/or by conducting space elements which are provided between adjacent terminals of the cells.
The invention takes into account that the terminals of individual battery cells of the battery module are electrically and thermally conducting and that spacer elements are preferably arranged in accordance with the invention between adjacent terminals of the cells. Since the circuit board of the battery management system can now brought into direct contact with the conducting elements of the battery cells the cabling between the individual battery cells and the battery management system which is otherwise required and which represents a source of faults is omitted. This has the consequence that not only sources of faults during the installation and operation of the battery management system in the vehicle are avoided but rather the assembly of the battery module is simplified. Moreover, corrosion at cable terminals is largely avoided since these are no longer present.
Since the battery management system now stands without cabling in direct contact with the individual battery cells of the battery module the function of the individual battery cells can be better monitored and controlled in a battery module. More precisely it is stated that the measured temperature and/or voltages of the individual battery cells can be more precisely determined and preferably also controlled.
The more precisely measured measurement values now mean that faults in the individual battery cells can now be more rapidly detected and/or more precise statements concerning the state of charge of the battery cells can be made, so that the battery management system if required can send a corresponding communication to the driver and/or to the evaluation device so that the driver is advised at an early stage when he has to drive to a charging station or an electrical socket or travel to a repair workshop.
In accordance with a preferred embodiment the terminals and/or the conducting spacer elements are arranged at one side of the battery module and form a contact plane in which the circuit board has electrical and/or thermal contact to the terminals or to the spacer elements.
This construction makes it possible to connect the circuit board directly to the conducting elements and optionally to screw it into place or to attach it with a suitable preload at the conducting elements.
It is particularly favorable when the housing of the battery module has a connection position for a battery management system which is preferably provided at the same side of the housing as the terminals of the battery cells. On installation of the battery module into a vehicle, the connection of the battery management system can now take place from one side of the battery which leads, on changing of the battery module and of the battery management system, to a simplified installation or removal, which not only results in a saving of time, but rather so simplifies the installation or removal that a mechanic can simply exchange a battery management system or a battery module as a module.
At the positions at which an electrical or thermal contact in the contact plane takes place one can directly measure the voltages and temperatures of the individual battery cells which favors the measurement accuracy.
In accordance with a further embodiment, the battery management system includes at least one interface, a processor, a flash memory, an analog/digital converter (ADC) and a power supply, with at least one of the interfaces preferably being an automotive interface.
It is particularly favorable when the battery management system has a processor which is able to process the ingoing and outgoing data of the battery management system. The processor can store this data in the flash memory and compare it with data which is stored on the flash memory. The measured data are as a rule analog data points which be digitalized for the more rapid calculation of the individual values by means of an analog/digital converter ADC. The measurement points can however also be directly detected in digital form. The values that are detected can be transferred by the interface to further devices in the vehicle. Since the battery management system has a separate power supply, the battery management system can also be used in vehicles which have not been used for a longer time interval, because the separate power supply ensures that the battery management system can also be used with a switched off battery module and the stored data of the battery management system is not lost and that the battery management system does not additionally discharge the battery cell which under some circumstances are empty, which would make the battery cell unusable.
Simple customary interface plugs or bus connectors can be used for the battery management system and the interface can be a CAN, LIN, RS485, uBus or any other kind of interface which can be used for the transmission of data.
In accordance with a further embodiment the battery management system is designed to measure voltage differences and/or a value proportional thereto at different points at the battery cell and optionally to store the measured voltages at least temporarily.
A potential difference between the positive and the negative terminals of a battery cell is preferably measured in order to obtain a pronouncement of the instantaneous state of charge of a battery cell. Since the voltage differences or voltages are at least temporarily stored, discharging rates and charging rates of the individual battery cells can be determined. This is above all useful when the charging rates or discharging rates for the individual battery cells set by the battery management system are exceeded or fallen short off because the battery management system can now transmit a warning or fault indication to the driver or to an evaluation device.
In accordance with a further embodiment the battery management system is designed to monitor the measured voltages of the battery cells.
The battery charging or discharging rates of individual battery cells can be stored in a memory and can periodically compared with one another. This is above all expedient than the charging or discharging cycles of the individual battery cells change with increasing working life because the battery management system can now estimate the remaining working life of the individual battery cells with respect to the stored characteristics and can if necessary transmit a warning signal or a fault signal to the driver or to an evaluation device give effect that the battery module change as expected.
In accordance with a further embodiment the battery management system is designed to monitor a charging process of the battery module with reference to the measured voltages of the battery cells and if necessary to regulate individually for each cell by changing resistances associated with the battery cells.
If the preset discharging and/or charging rates of the battery cells are fallen short of or exceeded, then the battery management system can regulate the charging procedure and/or the discharging procedure with reference to the resistances associated with the battery cells. Individual circuits can also be associated with the individual batteries which are for example able to change a current flow to the individual battery cells by transistors and/or diodes and thus to regulate it.
In accordance with a further embodiment the battery management system is designed in order to store temperatures measured at at least one point in the battery module if necessary at least temporarily.
The individual battery cells of a battery module are preferably operated and stored at temperatures in the range from 5° C. up to 30° C. The working life of the individual battery cells can also drop significantly when the temperatures of the battery cells exceed or fall short of these values. By at least temporarily storing the measured temperatures a heating and/or cooling rate of the battery module can be determined. This is above all useful when heating rates and/or cooling rates of the individual battery cells preset by the battery management system are fallen short of or exceeded in order to change these by suitable counter-measures.
In accordance with a further embodiment the battery management system is designed to monitor the measured temperatures. Since the battery management system monitors the measured temperatures it can also be ensured that, for example after a warming up phase of the battery cells these do not overheated and/or that the battery cells do not cool down too much and be correspondingly damaged as a result of low outer temperatures.
In accordance with a further embodiment the circuit board has heating resistors associated with the battery cells which serve to heat up battery cells and which preferably directly contact the conducting elements, i.e. the terminals of the battery cells or the conducting spacer elements.
The battery cells are preferably stored and/or operated at at least 5° C. Should the outer temperature be less than 5° C. and the battery cells not be in operation, then these can be heated via suitable heating resistances with a resistive heating system which is arranged at the terminals of the battery cells, with for example 1 Watt/h even with arctic temperatures and can thus be reliably operated.
In accordance with a further embodiment, the battery management system is designed to initiate a heating procedure when a temperature measured at a point of the battery cell amounts to less than 5° C. and/or the battery management system is then designed to initiate a cooling procedure when the measured temperature amounts to more than 30° C.
Should the temperatures exceed or fall short off certain values, then the battery management system can initiate a heating process and/or a cooling process via the cooling circuit. Typically the battery modules are surrounded by a cooling circuit which can cool the temperatures of the battery cell down to less than 30° C. and preferably cools them to a temperature between 5° C. and 30° C., in order to ensure that the battery cells do not suffer any long term damage because they were operated or stored at too high a temperature or too low a temperature. The coolant circuit is as a rule coupled to a heat exchanger and can also be used as a heating circuit. A heating system can also be provided in the circuit guiding the coolant which heats the coolant and hereby ensures the desired minimum temperature. The heating procedure can however also take place through the resistance heating which is arranged on the circuit board.
In accordance with a further embodiment, circuits are arranged on the circuit board for the monitoring of the temperatures and/or voltages. This makes it possible to measure as close as possible to the individual temperature measurement points or voltage measurement points, which has the consequence that the measured measurement values can be more accurately detected.
In accordance with a further embodiment, the individual circuits are arranged between the said contacts of the individual battery cells of the circuit board, in particular in the region of the circuit board between the terminals and/or between the conducting spacer elements of the battery cells. This makes it possible to obtain relatively short conductive tracks between the individual components and hereby reduces the influence of external sources of faults or scatter fields on the measured temperatures and voltages which would reduce the measurement accuracy.
In accordance with a further embodiment, the circuits are arranged in the area of the contact plane on the circuit board. This not only leads to compact assemblies which simplify the exchange of the battery module and/or battery management system if required, since the operator has more space available for the installation or removal.
In accordance with a further embodiment a signal processing device is arranged on the circuit board which is designed to convert the measured or monitored temperatures and/or voltages into digital signals which are evaluated in an evaluation unit. Through the analog/digital conversion it is avoided that the analog signal are distorted and that imprecise measured values are thereby supplied.
In accordance with a further embodiment, the signal processing device is designed to modulate the digital signals onto an output voltage of the battery cells and/or onto a output voltage of the battery module which is made available by connection lines of the battery module, whereby these digital signals from an evaluation unit can be detected via the detection cable of the battery module and optionally at least temporarily stored, with the evaluation unit preferably being decoupled from the circuit board. This could replace an interface of the battery management system, since now only the power cable of the individual battery module has to be used in order to transmit the measured signal to the evaluation unit, which simplifies the installation and removal of the battery module and/or of the battery management system and also minimizes the cabling complexity.
In accordance with a further embodiment contact between the battery management system and the battery module is produced by screws and/or spring contacts. This signifies that no solder joints are required in order to make a connection of the circuit board with the terminals of the battery cells or with the spacer elements between the terminals of the battery cells. This has the advantage that no cold solder joints can arise which could cause reliability problems in the battery management system.
In a further aspect of the invention a battery module unit is provided which consists of a combination of the battery management system of the invention and the battery module of the initially named kind which is characterized in that the terminals which are of areal design and provided with cutouts are arranged in at least two rows such that the broad sides of adjacent areal terminals of a respective row confront one another, in that the terminals of each row are held at a spacing from one another by systematically disposed conductive spacer elements and, if necessary, by insulating spacer elements, in that the cells are connected electrically in series and/or parallel to one another within the module by systematic arrangement of that positive and negative terminals in the one or other row and in that the terminals of each row and also the spacer elements arranged there between are pressed against one another by a clamping device.
A mechanical layout of the battery module of this kind makes it possible first of all, depending on the systematic arrangement of the positive and negative terminals of the cells within the module, to achieve different operating voltages and operating currents with a basically similar design of the battery module, so that most components can be used in the different variants and few special parts required, if at all, which would otherwise increase the manufacturing costs. It is also basically possible to select the number of the cells per battery module flexibly and nevertheless to use many common components in the manufacture of the respective battery modules. The battery size can be scaled by the modular concept and the electrical and hydraulic connection possibilities in wide ranges. The design principles can be rapidly and simply adapted with changed cell geometry or performance data to other flat cells.
The battery module unit in accordance with the invention can thus be flexibly designed and itself quasi has a modular construction.
Through the use of areal terminals it is possible, on the one hand, to make the individual cells, which are preferably of parallelepiped shape in plan view, relatively flat, whereby heat can be dissipated from the individual cells via the areal terminals. Through the flat parallelepiped shape of the cells which results through this heat can also be readily transferred away from the flat sides of the cell, whereby a precondition can be provided for attaining a tight temperature operating range in the cell. Since the terminals of each row can be pressed against one another by a respective clamping device or against spacer elements arranged therebetween, it can be ensured that resistance losses at the different terminals do not arise or only arise to a small degree and that the battery module always has the desired output voltage over the entire working life of the battery module corresponding to the respective state of charge, because constant circumstances prevail and changing ohmic losses are not to be expected.
It is particularly favorable when the areal terminals are formed by extensions of the electrodes of the cells and are designed for intentional heat dissipation from the cells for the active cooling of the cells and can be connected to a heat dissipating cooling device. In this way the leading away of heat from the interior of the cell is favored.